This invention relates to a plate thickness detection method and a plate thickness detection apparatus for a press which presses a workpiece by the cooperation of a punch and a die.
As a conventional plate thickness detection apparatus in a press or particularly in a press brake, there is known one described in, for example, Japanese Patent Application Laid-Open No. 10-180499. The press brake disclosed therein detects a pinching point at which an upper die contacts with a workpiece from a change in the torque of a servo motor which drives a hydraulic pump which supplies hydraulic oil to a hydraulic cylinder for driving a ram.
However, a plate thickness detection method for detecting a pitching point from a change in pressurizing side pressure in a hydraulic cylinder has the following disadvantages. Since a change point at which pressure rises is detected while a pressurizing side (cylinder head side) having a large cross-sectional area in the cylinder chamber is pressurized, it is difficult to detect the pressure change point particularly if a press becomes large in size.
Further, since the pressurizing side is pressurized, a pressure force acts on a workpiece and the workpiece is bent if the detection of the pinching point delays, whereby the plate thickness of the workpiece cannot be accurately detected.
This invention has been made in view of the above-stated disadvantages of the conventional art and an object of this invention is to provide a plate thickness detection method and a plate thickness detection apparatus in a press capable of accurately detecting thickness of a workpiece plate without bending the workpiece.
To attain the above object, a plate thickness detection method for a press according to the present invention in a first aspect, comprises the following steps of: descending a ram from a certain height position; detecting pressure of hydraulic oil discharged from a rod-side cylinder chamber at this time; detecting time at which a punch contacts with a workpiece on the die, from a change of the detected pressure; detecting upper and lower positions of the ram at this time; obtaining a plate thickness of the workpiece from the detected height position of the ram and a set height between the certain height known in advance and an upper surface of the die: and vertically moving the ram to which the punch is attached, based on the obtained plate thickness of the workpiece, and pressing the workpiece cooperatively by the punch and the die.
Accordingly, to detect the upper surface position of the workpiece based on which the plate thickness of the workpiece is detected, the ram is descended from a certain height position, the pressure of the hydraulic oil discharged from the rod-side cylinder chamber of the hydraulic cylinder at this time is detected, and the position at which the punch attached to the ram contacts with the workpiece is detected from a change of this detected pressure. Therefore, the change of the ram position is detected more sensitively than a case where the pressure of the cylinder-head side cylinder chamber having a large cross-sectional area in the cylinder chamber is detected. In addition, if the upper surface of the workpiece is detected, the plate thickness of the workpiece can be calculated from this detected upper surface position and a set height between the certain height position of the ram known in advance and the upper surface position of the die.
In a plate thickness detection method for a press according to the invention in a second aspect dependent on the first aspect, the ram is descended by a self-weight; the pressure of the hydraulic oil discharged from the rod-side cylinder chamber at this time is detected; and the time at which the punch contacts with the workpiece is detected from the change of the detected pressure.
With the above-stated constitution, the ram to which the punch is attached is descended by the self-weight, and the time at which the punch contacts with the workpiece is detected from a change of the pressure of the hydraulic oil discharged from the rod-side cylinder chamber at this time. While the ram is being descended, the hydraulic oil is not forced into the cylinder head-side cylinder chamber and sucked by negative pressure which is generated by the descent of the piston.
Accordingly, even if the detection that the punch contacts with the workpiece is delayed only the self-weight of the ram and the like acts on the workpiece and it is thereby possible to prevent the workplace from being bent
In a plate thickness detection method for a press according to the invention in a third aspect dependent on the first or second aspect, if the ram is to be descended by the self-weight, the ram is descended at a speed equal to or lower than a ram self-weight maximum falling speed at which the workpiece is not bent even if the punch contacts with the workpiece.
Accordingly, if the ram is to be descended by the self-weight, the ram is descended at a speed equal to or lower than a ram self-weight maximum falling speed at which the workpiece is not bent even if the punch contacts with the workpiece. Therefore, it is possible to prevent the workpiece from being bent even if the punch contacts with the workplace.
In a plate thickness detection method for a press according to the invention in a fourth aspect dependent on one of the first to third aspects, time at which the pressure of the hydraulic oil discharged from the rod-side cylinder chamber changes from the pressure by the self-weight to atmospheric pressure is detected as the time at which the punch contacts with the workpiece.
With the above-stated constitution, the pressure of the hydraulic oil discharged from the rod-side cylinder chamber detected when the ram is descended, is the pressure following the descent caused by the self-weight of the ram, the punch and the like. However, if the punch contacts with the workpiece, the pressure by the self-weight is eliminated, so that atmospheric pressure is detected. Therefore, it is possible to determine that the punch contacts with the workpiece when this atmospheric pressure is detected.
A plate thickness detection method for a press according to the invention in a fifth aspect, comprises the following steps of: descending a ram from a certain height position while controlling a descent speed, and detecting a ram descent position; detecting a ram stop position from a change of this detected ram position: determining the detected stop position as a position at which a punch contacts with a workpiece on the die; obtaining a plate thickness of the workpiece from the ram position which is determined as the position at which the punch contacts with the workpiece, and from a set height of a difference between the certain height known in advance and an upper surface of the die; and vertically moving the ram, to which the punch is attached, based on the obtained plate thickness of the workpiece, and pressing the workpiece cooperatively by the punch and the die.
Accordingly, to detect the upper surface position of the workpiece based on which the plate thickness of the workpiece is detected, the ram is descended from a certain height position while controlling a descent speed, a stop position is detected from a change of the ram descent position and this stop position is determined as the upper surface of the workpiece. Therefore, the change of the ram position is detected more sensitively than a case where the pressure of the cylinder-head side cylinder chamber having a large cross-sectional area in the cylinder chamber is detected. In addition, if the upper surface of the workpiece is detected, the plate thickness of the workpiece can be calculated from this upper surface position and a set height between the certain height position of the ran known in advance and the upper surface position of the die.
A plate thickness detection apparatus in a press according to the invention in a sixth aspect, comprises: ram position detection means for detecting upper and lower positions of a ram to which a punch is attached; oil pressure detection means for detecting pressure of hydraulic pressure discharged from a rod-side cylinder chamber of a hydraulic cylinder which vertically moves the ram; a determination section detecting a position at which the punch contacts with a workpiece, from a change of the pressure detected by the oil pressure detection means; and a plate thickness calculation section calculating a plate thickness of the workpiece, from the ram position which is determined by the determination section as position at which the punch contacts with the workpiece and from a set height of a difference between a certain height of the ram known in advance and an upper surface of the die, whereby the ram is vertically moved by the hydraulic cylinder and the workpiece is pressed cooperatively by the punch and the die.
Accordingly, to detect the upper surface position of the workpiece based on which the plate thickness of the workpiece is detected, the oil pressure detection means detects the pressure of the hydraulic oil discharged from the rod-side cylinder chamber of the hydraulic cylinder which vertically moves the ram, the determination section detects the position at which the punch attached to the ram contacts with the workpiece from a change of this detected pressure, and the ram position detection means detects the upper and lower positions of the ram at this time. Therefore, the change of the ram position is detected more sensitively than a case where the pressure of the cylinder-head side cylinder chamber having a large cross-sectional area in the cylinder chamber is detected. In addition, if the upper surface of the workpiece is detected, the plate thickness calculation section calculates the plate thickness of the workpiece based on a set height of a difference between the certain height position of the ram known in advance and the upper surface of the die.
A plate thickness detection apparatus in a press according to the invention in a seventh aspect dependent on the sixth aspect, further comprises: a ram self-weight maximum falling speed calculation section calculating a ram self-weight maximum falling speed at which the work is not bent even if the punch contacts with the workpiece if the ram is to be descended by a self-weight.
With the above-stated configuration, the ram self-weight maximum falling speed calculation section calculating a ram self-weight maximum falling speed at which the work is not bent even if the punch contacts with the workpiece if the ram is to be descended by a self-weight.
Therefore, even if the punch abuts on the workpiece by the descent of the ram, it is possible to prevent the workpiece from being bent.
A plate thickness detection apparatus in a press according to the invention in an eighth aspect, which vertically moves a ram, to which a punch is attached, by a hydraulic cylinder actuated by hydraulic oil from a two-way pump and which presses a workpiece cooperatively by the punch and a die, comprises: ram position detection means for detecting upper and lower positions of the ram; oil pressure detection means, provided halfway along a hydraulic circuit which connects a rod-side cylinder chamber of the hydraulic cylinder which vertically moves the ram, to the two-way pump, for detecting pressure of the hydraulic oil discharged from the rod-side cylinder chamber; a determination section determining a position at which the punch contacts with the workpiece, from a change of the pressure of the hydraulic oil detected by the oil pressure detection means; and a plate thickness calculation section calculating a plate thickness of the workplace, from a ram position which is determined by the determination section as the position at which the punch contacts with the workpiece and from a set height of a difference between a certain height of the ram and an upper surface of the die.
Accordingly, to detect the upper surface position of the workpiece based on which the plate thickness of the workpiece is detected, the oil pressure detection means detects the pressure of the hydraulic oil discharged from the rod-side cylinder chamber of the hydraulic cylinder which vertically moves the ram, the determination section detects the position at which the punch attached to the ram contacts with the workpiece from a change of this detected pressure, and the ram position detection means detects the upper and lower positions of the ram at this time. Therefore, the change of the ram position is detected more sensitively than a case where the pressure of the cylinder-head side cylinder chamber having a large cross-sectional area in the cylinder chamber is detected. In addition, if the upper surface of the workpiece is detected, the plate thickness calculation section calculates the plate thickness of the workpiece based on a set height of a difference between the certain height position of the ram known in advance and the upper surface of the die.
In a plate thickness detection apparatus in a press according to the invention in a ninth aspect dependent on the eighth aspect, the oil pressure detection means detects the pressure of the hydraulic oil discharged from the rod-side cylinder chamber when a speed switch valve provided halfway along the hydraulic circuit is switched to discharge the hydraulic oil from the rod-side cylinder chamber to the two-way pump and to descend the ram by a self-weight.
With the above-stated constitution, the ram to which the punch is attached is descended by the self-weight and the speed switch valve is switched, the pressure of the hydraulic oil discharged from the rod-side cylinder chamber at this time is detected by the oil pressure detection means and the time at which the punch contacts with the workpiece is detected from a change of the detected pressure. While the ram is being descended, the hydraulic oil is not forced into the cylinder head-side cylinder chamber and sucked by negative pressure which is generated by the descent of the piston.
Accordingly, even if the detection that the punch contacts with the workpiece is delayed, only the self-weight of the ram and the like acts on the workplace and it is thereby possible to prevent the workpiece from being bent.
In a plate thickness detection apparatus in a press according to the invention in a tenth aspect dependent on the eighth or ninth aspect, the determination section determines that time at which the pressure of the hydraulic oil discharged from the rod-side cylinder chamber detected by the oil pressure detection means changes from the pressure by a self-weight to atmospheric pressure, as time at which the punch contacts with the workpiece.
Accordingly, the pressure of the hydraulic oil discharged from the rod-side cylinder chamber detected by the oil pressure detection means when the ram is descended, is the pressure following the descent caused by the self-weight of the ram, the punch and the like. However, if the punch contacts with the workpiece, the pressure by the self-weight is eliminated, so that the oil pressure detection means detects atmospheric pressure. Therefore, the determination section can determine that the punch contacts with the workpiece when this atmospheric pressure is detected.
A plate thickness detection apparatus in a press according to the invention in an eleventh aspect dependent on one of the eighth to tenth aspect, further comprises: a ram self-weight maximum falling speed calculation section calculating a ram self-weight maximum falling speed at which the workpiece is not bent even if the punch contacts with the workpiece if the ram is to be descended by the self-weight.
With the above-stated constitution, the ram self-weight maximum falling speed calculation section calculates a ram self-weight maximum falling speed at which the workpiece is not bent even if the punch contacts with the workpiece if the ram is to be descended by the self-weight, and the ram is descended at a falling speed which does not exceed the ram self-weight maximum falling speed.
So, the workpiece is prevented from being bent even though the workpiece is abutted by the punch with the falling ram.
A plate thickness detection apparatus in a press according to the invention in a twelfth aspect, which apparatus vertically moves a ram, to which a punch is attached, and which presses a workpiece cooperatively by the punch and a die, comprises: ram position detection means for descending the ram from a certain height position while controlling a descent speed, and for detecting a ram descent position; a determination section detecting a ram stop position from a change of the ram position detected by the ram position means, and determining this detected stop position as a position at which the punch contacts with the workpiece; and a plate thickness calculation section calculating a plate thickness of the workpiece, from the ram position determined by the determination section as the position at which the punch contacts with the workpiece and from a set height of a difference between the certain height known in advance and an upper surface of the die.
In the plate thickness detection apparatus, therefore, to detect the upper surface position of the workpiece based on which the plate thickness of the workpiece is detected, the ram is descended from a certain height position and by the ram position detection means detects the ram position, the determination section detects a stop position from a change of this detected ram position and determines this stop position as the upper surface of the workpiece. Therefore, the change of the ram position is detected more sensitively than a case where the pressure of the cylinder-head side cylinder chamber having a large cross-sectional area in the cylinder chamber is detected. In addition, the plate thickness calculation section obtains the plate thickness of the workpiece from the detected upper surface position of the workpiece and a set height of a difference between the certain height position of the ram known in advance and the upper surface of the die.